Add some testing

src/test/java/org/bukkit/GrassSpeciesTest.java

@@ -0,0 +1,15 @@
+package org.bukkit;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import org.junit.Test;
+
+public class GrassSpeciesTest {
+    @Test
+    public void getByData() {
+        for (GrassSpecies grassSpecies : GrassSpecies.values()) {
+            assertThat(GrassSpecies.getByData(grassSpecies.getData()), is(grassSpecies));
+        }
+    }
+}